1,721,486 research outputs found
38. Raven (J. Ε.). Plato's thought in the making
No full textMoreau Joseph. 38. Raven (J. Ε.). Plato's thought in the making. In: Revue des Études Grecques, tome 79, fascicule 374-375, Janvier-juin 1966. pp. 545-546
Kirk (G. S.) & Raven (J. E.). The Presocratic Philosophers
No full textBergmans Simone. Kirk (G. S.) & Raven (J. E.). The Presocratic Philosophers. In: Revue belge de philologie et d'histoire, tome 37, fasc. 4, 1959. Histoire (depuis la fin de l'Antiquité) — Geschiedenis (sedert de Oudheid) pp. 1061-1064
Biomineralisation by photosynthetic organisms: evidence of co-evolution of the organisms and their environment?
No full textBiomineralization is widespread among photosynthetic organisms in the ocean, in inland waters and on land.
The most quantitatively important biogeochemical role of land plants today in biomineralization is silica
deposition in vascular plants, especially grasses. Terrestrial plants also increase the rate of weathering, providing
the soluble substrates for biomineralization on land and in water bodies, a role that has had global biogeochemical
impacts since the Devonian. The dominant photosynthetic biomineralizers in today’s ocean are diatoms and
radiolarians depositing silica and coccolithophores and foraminifera depositing calcium carbonate. Abiotic
precipitation of silica from supersaturated seawater in the Precambrian preceded intracellular silicification
dominated by sponges, then radiolarians and finally diatoms, with successive declines in the silicic acid concentration
in the surface ocean, resulting in some decreases in the extent of silicification and, probably, increases in
the silicic acid affinity of the active influx mechanisms. Calcium and bicarbonate concentrations in the surface
ocean have generally been supersaturating with respect to the three common calcium carbonate biominerals
through geological time, allowing external calcification as well as calcification in compartments within cells or
organisms. The forms of calcium carbonate in biominerals, and presumably the evolution of the organisms that
produce them, have been influenced by abiotic variations in calcium and magnesium concentrations in seawater,
and calcium carbonate deposition has probably also been influenced by carbon dioxide concentration whose
variations are in part biologically determined. Overall, there has been less biological feedback on the availability
of substrates for calcification than is the case for silicification
Raven J. et Walters M. — Mountain flowers. Londres, The New Naturalist, volume 33, Collins, 1956
No full textBourlière François. Raven J. et Walters M. — Mountain flowers. Londres, The New Naturalist, volume 33, Collins, 1956. In: La Terre et La Vie, Revue d'Histoire naturelle, tome 11, n°1, 1957. pp. 97-98
14. Kirk (G. S.), Raven (J. E), Schofield (M.), The Presocralic Philosophers
No full textDemont Paul. 14. Kirk (G. S.), Raven (J. E), Schofield (M.), The Presocralic Philosophers. In: Revue des Études Grecques, tome 99, fascicule 472-474, Juillet-décembre 1986. pp. 383-384
Algae
No full textAlgae frequently get a bad press. Pond slime is a problem in garden pools, algal blooms can produce toxins that incapacitate or kill animals and humans and even the term seaweed is pejorative — a weed being a plant growing in what humans consider to be the wrong place. Positive aspects of algae are generally less newsworthy — they are the basis of marine food webs, supporting fisheries and charismatic marine megafauna from albatrosses to whales, as well as consuming carbon dioxide and producing oxygen. Here we consider what algae are, their diversity in terms of evolutionary origin, size, shape and life cycles, and their role in the natural environment and in human affairs
Nitrogen and sulfur assimilation in plants and algae
No full textNitrogen and Sulfur are abundant constituent of plant and algal cells that are assimilated at the lowest oxidation number, as NH4+ and S2-, although they can be acquired with their highest oxidation number, as NO3- and SO42-. Some occasional differences and variants exists for transport and assimilation systems; the greatest differences in the way vascular plants and algae use N and S, however, most probably resides in regulation. For instance, nitrate assimilation in plants is strongly regulated by phosphorylation. In algae, redox regulation appears to be more important. Similarly, sulfate reduction has its main control step at the level of APS reductase in higher plants, whereas in algae a redox regulation has been recently been hypothesized for ATP sulfurylase, the first step in sulfate assimilation. Unfortunately, the information on the regulation of N and S acquisition and assimilation is limited to very few species (e.g. Chlamydomonas reinhardtii) this is especially true in the case of sulfur. This review attempts to highlight the points of divergence in N and S utilization by plants and algae, leaving aside the biochemical details and the features that do not show any obvious difference
Fashion and Female Beat Identity in the Writing of Jones, Johnson, and di Prima
Full text linkIn her article Fashion and Female Beat Identity in the Writing of di Prima, Johnson, and Jones Raven J. See discusses how the women writers of the Beat Generation have become iconically defined by their fashion choices. Clothing and accessories offer Beat women a means to construct and express their identity and Diane di Prima, Joyce Johnson, and Hettie Jones write about fashion in their narratives of self-creation. Like their male contemporaries, Beat women make style choices that allow them to reject mainstream culture and identify within Beat subculture. However, these women write about their decisions to accept or reject certain styles in particularly female terms. Their discussion of fashion is also a discussion of female embodiment, and their fashion choices are often assertions of control over their own bodies
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